Portable MBR success at megaproject site

01 December 2012

ACWA Emirates has reported excellent results from a portable membrane bioreactor sewage treatment plant that is purifying waste for a $9 billion gas megaproject at Habshan, a remote desert region of the Middle East.

The company, part of ACWA Services, installed the state-of-the-art plant on behalf of CCC Contractors at the Habshan 5 gas complex, and has been undertaking operations and maintenance since start-up.

Habshan 5 is a gas processing and sulphur production facility, around 150km south west of Abu Dhabi, which will process 1000 million cubic feet per day of gas from the offshore Umm Shaif facility and a further equivalent amount of onshore gas. When completed, the site will provide 270MW of much-needed power to meet UAE’s fast-growing demand.

The Abu Dhabi Gas Industries (GASCO) site is now over 90% complete, but the demanding construction process has meant the site requires large numbers of workers – around 5000 in all. Such camps act as home, often for several years, to a fully-fledged, self-contained community that is a vital element in establishing and operating such major projects on extremely remote sites.

The challenge was to provide effective wastewater services to the equivalent of a small town in such an isolated area.

The portable MBR plant consists of two containerised Memtreat® units, which treat roughly half of the flow each (with an average flow of 501m3 through MBR1 and 480m3 through MBR 2). On some days the treatment plant has capably surpassed its 1000m3 design flow thanks to the ability of the MBR system to cope well with widely varying flows.

The advanced Memtreat® treatment process provides an extremely high quality treated effluent within a small footprint, and does not require clarification stages or tertiary treatment processes. It also produces less sludge than a conventional secondary treatment process, further reducing its environmental impact.

The final effluent from the membranes is of such a high quality that it is suitable for direct discharge without further treatment, or for reuse in irrigation, cooling, or a variety of industrial processes.

Because the units are portable, they can be relocated to a different part of the site if required, or ultimately used on another project.

There were challenging issues on the Habshan 5 site that had to be tackled such as low wastewater flows, and oil, grease and chemicals entering the system from the kitchen, shower and toilet facilities. ACWA Emirates returned to the source of each challenge for an optimal solution, installing oil and grease traps in the kitchens and ensuring plant operators checked the surface of the balance tanks for oil and grease buildups.

Dealing with the chemicals entering the wastewater system involved monitoring the types of products used by the cleaning staff to ensure they did not impact the plant’s operation, and close control means the plant has always worked to its optimum performance.

To date, the plant has treated over 585,000m3 of wastewater, at an average of 685m3/day. The highly-treated effluent from the portable MBR is stored in a holding tank and transferred by tanker for use in toilet flushing, dust dampening, concrete batches and trench backfilling. Around 10,000 gallons of sludge are removed every three days to maintain a healthy level of Mixed Liquor Suspended Solids (MLSS).

The cost savings achieved using the portable MBR solution are considerable. Removing the wastewater by tanker from such a remote site to the nearest treatment facility, 100km away, and bringing in water for wastewater treatment, would have cost an estimated AED 42 million ($11.43 million, £7.1 million), equivalent to AED2700 ($735, £500) for each round of delivery and removal by tanker.

Factoring in the investment costs of the plant, tank, pipelines, pumping stations, operation and maintenance, chemicals and labour, the net financial savings are estimated at AED 10 million ($2.7 million, £1.7 million). The ability to avoid moving water and wastewater by tanker also has significant environmental benefits in terms of reduced fuel consumption and environmental damage.

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